Kinetics of CO2 Sorption using ZK-4 zeolite

https://doi.org/10.1021/acsomega.0c03749

“We followed the physisorption of CO₂ by monitoring the development of the υ₁ + υ₃ and υ₁ + 2υ₂ combination band at 3317 cm^–1 with respect to time on zeolites Na-ZK-4 (1.8 and 2.8), NaK-ZK-4 (1.8), 28 at. % K⁺ (the sample with the highest CO₂selectivity at Si/Al = 1.8), and NaK-ZK-4 (2.8), 55 at. % K⁺ (the sample with the highest CO₂ selectivity at Si/Al = 2.8); see Figure 7. The zeolite Na-ZK-4 (2.8) had the fastest uptake of CO₂, as shown in Figure 7, which was expected as it had only Na⁺ ions, which made the passage of CO₂ more easy than that if K⁺ ions were present. The physisorption of CO₂ on zeolite Na-ZK-4 (2.8) reached 60% of its maximum capacity already after 10 s. In the other two samples, the reduced CO₂ physisorption rates were due to K⁺ ions populating the 8-rings. Specifically, zeolite NaK-ZK-4 (1.8) with 28 at. % of K⁺ had the slowest uptake of CO₂, which took 10 min to reach 80% of its maximum CO₂ physisorption capacity (i.e., after 24 h). This slow uptake rate was related to that K⁺ ions were present in the 8-rings of this zeolite and that the 6-rings were populated by Na⁺ and K⁺ ions. The CO₂ adsorbing more rapidly on zeolite NaK-ZK-4 (2.8) 55 at. % than on zeolite NaK-ZK-4 (1.8) 28. at. % was ascribed to the smaller amount of Na⁺ and K⁺ cations in the 6-rings in the zeolite with a Si/Al ratio of 2.8.”

“Figure 7. Kinetics of CO₂ physisorption on zeolites Na-ZK-4 (1.8, 2.8), NaK-ZK-4 (1.8) 28 at. %, and NaK-ZK-4 (2.8) 55 at. %.”